The tires of a vehicle are among the systems most critical to driving safety during operation of the vehicle. A sudden pressure decrease, which regularly occurs as an indication of tire damage, can result in limited road adhesion and, in some cases, can render the vehicle no longer controllable. At high speeds, in particular, tire pressure losses can therefore have an extremely devastating effect. Prompt detection of a defective tire can thus make a considerable contribution to driving safety.
Systems which monitor the state of a tire, in particular the air pressure, are known in the art. In addition to direct determination of the air pressure of a tire, the rotation speeds of the wheels can be employed in order to determine a change in tire pressure. For example, changes in the rotation speeds of individual wheels can be sensed and used to demonstrate a change in the operating state of the tires.
Published German patent documents DE 36 10 116 and DE 32 36 520 describe monitoring systems which indicate the tire state in the context of specific operating states (traveling straight ahead without deceleration or acceleration). These documents also describe a normalization of the rotation speeds to the respective vehicle speed.
For indirect-measurement tire-pressure monitoring systems, the use of differences in wheel rotation speeds of individual wheels for tire state detection is known, for example, from European Patent 0 291 217. In such systems, pressure losses can be ascertained by way of the deviation in wheel speeds in the context of a reduced tire circumference.
Published German Patent Application 199 44 391 describes the adaptation of a calibration value serving to monitor tire pressure. In this method, a recalibration of the tire pressure system is performed on the basis of a modified operating state of the tire, the old value being overwritten.